Secondary batteries employing tubular plate construction generally exhibit superior electrical capacity to weight ratios when compared to similarly sized secondary batteries employing conventional flat pasted grids. This desirable phenomenon primarily occurs because the tube-type electrode design exposes a substantially greater surface area of active material to the electrolyte contained within the battery. Accordingly, since the electrolyte is able to freely circulate about the tubes and through the porous tube sheaths that contain more material, the tubular plate battery is capable of delivering higher capacities. In addition, by securely enveloping the active material in the porous but rigid sheath, the tubular plate battery is better protected from the deleterious effects caused by shocks and vibration.
In brief, tubular plate batteries generally include positive plates characterized by a lead alloy grid having a series of spaced, electrically conductive spines appended to a first electrically conductive cross member. A porous, rigid sheath envelopes each spine to form a plurality of hollow tubes. Each tube, packed with active material, is bottom sealed and connected to adjoining tubes by a second nonconductive cross member. Generally, the negative plates are conventional pasted plates.
As with most secondary battery designs, the positive (tubular) plates and the negative plates are disposed in an alternating spaced relationship within the battery case. A separator is positioned between the plates. Moreover, a number of positive plates and negative plates are electrically ganged together (positive to positive, negative to negative) to form a cell. A plurality of interconnected cells constitute a battery.
Initially, the sheaths were made from slotted hard rubber but over the years, battery designers have turned to woven plastic and braided glass sheaths to provide superior service. Indeed, some present day glass sheaths are made by saturating a glass braid with an alcohol/phenolic solution and then passing the saturated sheath over a shaping mandrel in the presence of radiant heaters to drive off the alcohol in vapor form. After the sheath is rough cut to a desired length (anywhere from about 4 inches [10.6 cm] to about 28 inches [71.12 cm]), the sheath is dipped into a dilute alcohol/phenolic solution to increase resin pick-up whereupon, it is then baked in an oven. The sheath is then dipped for a second time and baked again for approximately a half hour.
It should be readily apparent from the foregoing discussion that this method is both energy intensive and a source of industrial pollution. Moreover, large quantities of expensive solvent are necessary to effect a stiff tube with a specified resin content.
Indeed, the aforementioned process of making tubular sheaths is running into the combined problems posed by: (1) increasingly stringent regulations restricting the amount of air pollution caused by solvent effluents; (2) the constantly escalating cost of energy; (3) the rising cost of expensive organic solvents; and (4) the flammable nature of the alcohol solution.
Clearly a more economic and practical method for manufacturing tube sheaths is desirable.